Gas turbine engines are known to include a compressor section for supplying a flow of compressed combustion air, a combustor section for burning fuel in the compressed combustion air, and a turbine section for extracting thermal energy from the combustion air and converting that energy into mechanical energy in the form of a rotating shaft.
Modern high efficiency combustion turbines have firing temperatures that exceed about 1,000° C., and even higher firing temperatures are expected as the demand for more efficient engines continues. Many components that form the “hot gas path” combustor and turbine sections are directly exposed to aggressive hot combustion gasses, for example, the combustor liner, the transition duct between the combustor and turbine sections, and the turbine stationary vanes and rotating blades and surrounding ring segments. In addition to thermal stresses, these and other components are also exposed to mechanical stresses and loads that further wear on the components.
Furthermore, many of the cobalt and nickel based super-alloy materials traditionally used to fabricate the majority of combustion turbine components used in the hot gas path section of the combustion turbine engine must be aggressively cooled and/or insulated from the hot gas flow in order to survive long term operation in this aggressive high temperature combustion environment.
Notwithstanding these protective efforts, the combustion turbine components nonetheless tend to suffer operational damage such as thermal fatigue, oxidation, corrosion, creep, foreign object damage, and the like, which typically causes cracking and spallation of the super-alloy substrate and/or protective ceramic coating. Since these high temperature resistant components are quite expensive, it is often desirable to repair or refurbish parts in order to extend their useful life.